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The formation and dynamics of cold-dome northeast of Taiwan

Seminar report. The formation and dynamics of cold-dome northeast of Taiwan. 報告人：沈茂霖 (Mao-Lin Shen) 2014/10/9. Outlines. Domain describtion Observations Numerical results and mechanic discussions Conclusions. NMHC. MHC. Numerical Model. Fig. 1b. Schematic of the study region.

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The formation and dynamics of cold-dome northeast of Taiwan

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  1. Seminar report The formation and dynamics of cold-dome northeast of Taiwan 報告人：沈茂霖 (Mao-Lin Shen) 2014/10/9

  2. Outlines • Domain describtion • Observations • Numerical results and mechanic discussions • Conclusions

  3. NMHC MHC Numerical Model Fig. 1b. Schematic of the study region.

  4. Observations • Microwave (MW) and InfraRed (IR) merged Sea Surface Temperature (SST) provided by Remote Sensing Systems (RSS) • MW and IR merged SST data available on 0.09°×0.09° spatial resolution over the global region (±90°) . • Time-longitude SST anomalies in the north of Taiwan and four events were checked. • Argo data.

  5. 2007 2008 2009 Fig. Time-longitude plot of SST anomalies in the north of Taiwan (25.4°N-25.9°N).

  6. Observations 1 Oct 2007 18 Oct 2007 23 Sep 2008 16 May 2008 Fig. 2. SST results.

  7. Observations Day 157 Day 226 Fig. 3. The temperature contour and velocity fields at depth 6m on day 157 and 226, Year 37.

  8. Observations Fig. 4. The Argo data since 3 Aug 2001 to 6 Sep 2009, and only 2047 data are available.

  9. Observations Fig. 5. The Argo data measured on Kuroshio main stream, in which has maximum salinity larger than 34.7 [Chuang et al, 1993], totally 9 profiles in JJA.

  10. Observations Fig. 7. Argo data taken from the float WMO No. 2900797.

  11. Observations Fig. 8. Argo data taken from the float WMO No. 2900819. Typhoon Kalmaegi 7/16~7/18

  12. Observations • Many events (local winds variation, typhoons, or winter intrusion of Kuroshio) merged with the cold-dome variation and make the analysis difficult. • Fewer field measures to have a good comprehension. • Lack of current velocities. Few information was carried by Argo trajectories. • Of WMO No. 2900797, the vertical temperature difference are about 3-5℃ on 12 Dec and 16 Dec .

  13. Numerical results • No special events interrupted. • Current velocities clearly identified. • Three spots were considered: Taiwan Strait Water (TSW), Cold-Dome Water (CDW), Kurioshio Surface Water (KSW). • Temperature variation • Motion of water parcel • Influence of topography change • Effect of wind-driven upwelling

  14. Numerical results Fig. 12. Temperature comparison of the three selected boxes. Upper 30 m averaged was taken.

  15. Numerical results Fig. Motion of flow particle in Kuroshio Subtropical Water.

  16. Topography change Origional (FO) Depth = 100 m (F100) Depth = 80 m (F080) Depth = 60 m (F060) Fig. Comparison of flow field and temperature contour of different topography.

  17. Topography change TSW CDW KSW Fig. 16. Temperature comparison among three marked region of the four numerical experiments.

  18. Numerical results (a) (b) Fig. (a) upwelling velocities of TWS and CDW, and (b) the wind-induced temperature difference variation.

  19. Numerical results Fig. 13. Temperature difference comparison: (a) the total one of TSW and CDW; (b) the convection-induced one of TSW and CDW; (c) the vertical temperature difference on depth 6 m and on depth 54 m of TSW, CDW, and KSW, respectively.

  20. Numerical results Fig. Cross-correlation of temperature difference: blue line, the total one and the convection one; red line, the total one and the turbulent diffusive one.

  21. Numerical results Day 157 Day 226 Fig. 3. The temperature contour and velocity fields at depth 6m on day 157 and 226, Year 37.

  22. Conclusions • Formation of cold-dome of northeast Taiwan is combined by many regional effects, such Kuroshio axis migration, topography change, wind-driven upwelling, vortex shedding, ocean surface mixing. • Main mechanics of the formation was verified by numerical experiments, in which special events were not considered. • Wind-driven upwelling introduces little temperature variation except typhoon events.

  23. Conclusions • Topography plays a main role in this region. Numerical experiments show that TSW dominates northeast Taiwan while bathymetry shallower than original one. • Convection has faster influence, and turbulent diffusion has more contribution. However, it also denotes the cold-dome can be disturbed easily. • The cyclonic eddy reserves the cold water.

  24. Thank you for your attention.

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